Functional Optical Hemodynamic Imaging of the Olfactory Cortex

Abstract

We used multichannel near-infrared spectroscopy (MNIRS) to monitor the activity of the frontal cortex as mirrored by hemodynamic responses subjected to olfactory stimulation. The aim of this study was to clarify the functional brain imaging of olfactory activity. Prospective study. This study was conducted on eight healthy subjects aged from 22 to 39 years (4 men and 4 women; mean age, 28.8 yr). We used a 22-channel near-infrared spectroscopy device with eight light-incident fibers and seven detector fibers, each with an interoptode distance of 2.5 cm on the frontal region. Olfactory stimulation consisted of five repetitions, each lasting 5 seconds and followed by a 55 seconds rest period. Isovaleric acid was used as odor stimulation, and saline was used as a control. We measured the changes in concentrations of oxyhemoglobin [oxyHb], deoxyhemoglobin [deoxyHb], and total hemoglobin [totalHb] from prebaseline values. Furthermore, we divided the frontal cortex into four areas (right upper, left upper, right lower, left lower) and investigated the activity in each area. Isovaleric acid caused changes, especially in the lower area, but saline caused no changes. [oxyHb] and [totalHb] increased after odor stimulation, but [deoxyHb] did not change. These active areas may be related to the orbitofrontal cortex, corresponding to olfactory cortices. This study has shown that MNIRS enables evaluation of changes in hemodynamics related to brain activity by olfactory stimulation.